Use of bispecific antibodies (bsAbs) to redirect effector T cells for the targeted killing of tumor cells has shown considerable promise both pre-clinically and clinically (see, e.g., Topp et al., 2012, Blood 120:5185-87; Bargou et al., 2008, Science 321:974-77). The bispecific antibodies developed to date contain a first binding site specific to CD3 for T-cell recruitment and activation and a second binding site for a targeted disease-associated antigen, such as CD19 (Bassan, 2012, Blood 120:5094-95). The bispecific antibody brings CD3+ T cells into direct contact with targeted disease cells and induces cell-mediated cytotoxicity (Bassan, 2012). Anti-CD3× anti-CD19 bispecific antibodies have been reported to produce a complete and durable molecular remission at very low concentrations in approximately 70% of adult patients with MRD+ ALL (Topp et al., 2012, Blood 120:5185-87). Bispecific antibodies recognizing gliomas and the CD3 epitope on T cells have been successfully used in treating brain tumors in human patients (Nitta, et al. Lancet 1990; 355:368-371).
Leukocyte redirecting bsAbs are not limited to T cells. The bispecific killer engagers (BiKEs) comprising scFvs against the NK cell antigen CD16 and a tumor-associated antigen (e.g., CD19, CD22, CD33) have also shown potent anti-cancer activity (e.g., Miller, Hematology Soc Hematol Educ Pogram 2013:247-53). Other alternatives include trispecific killer engagers (TriKEs), such as anti-CD16× anti-CD19× anti-CD22 (Miller, 2013; Gleason et al., 2012, Mol Cancer Ther 11:2674-84). An anti-CD16× anti-CD33 BiKE was used to treat AML and myelodysplastic syndrome (Miller, 2013; Wiernik et al., 2013, Clin Cancer Res 19:3844-55). In refractory AML, a CD16× CD33 BiKE led to potent tumor cell killing and cytokine production by NK cells. Inhibition of ADAM17 enhanced the CD16× CD33 BiKE response (Miller, 2013). Other trispecific, trivalent constructs, for example against CD16/CD19/HLA-DR, have been reported (Schubert et al., 2012, mAbs 4:45-56).
Numerous methods to produce bispecific antibodies are known (see, e.g. U.S. Pat. No. 7,405,320). Bispecific antibodies can be produced by the quadroma method, which involves the fusion of two different hybridomas, each producing a monoclonal antibody recognizing a different antigenic site (Milstein and Cuello, Nature 1983; 305:537-540). The fused hybridomas are capable of synthesizing two different heavy chains and two different light chains, which can associate randomly to give a heterogeneous population of 10 different antibody structures of which only one of them, amounting to ⅛ of the total antibody molecules, will be bispecific, and therefore must be further purified from the other forms. Fused hybridomas are often less stable cytogenetically than the parent hybridomas, making the generation of a production cell line more problematic.
Another method for producing bispecific antibodies uses heterobifunctional cross-linkers to chemically tether two different monoclonal antibodies, so that the resulting hybrid conjugate will bind to two different targets (Staerz, et al. Nature 1985; 314:628-631; Perez, et al. Nature 1985; 316:354-356). Bispecific antibodies generated by this approach are essentially heteroconjugates of two IgG molecules, which diffuse slowly into tissues and are rapidly removed from the circulation. Bispecific antibodies can also be produced by reduction of each of two parental monoclonal antibodies to the respective half molecules, which are then mixed and allowed to reoxidize to obtain the hybrid structure (Staerz and Bevan. Proc Natl Acad Sci USA 1986; 83:1453-1457). An alternative approach involves chemically cross-linking two or three separately purified Fab′ fragments using appropriate linkers. All these chemical methods are undesirable for commercial development due to high manufacturing cost, laborious production process, extensive purification steps, low yields (<20%), and heterogeneous products.
Discrete VH and VL domains of antibodies produced by recombinant DNA technology may pair with each other to form a dimer (recombinant Fv fragment) with binding capability (U.S. Pat. No. 4,642,334). However, such non-covalently associated molecules are not sufficiently stable under physiological conditions to have any practical use. Cognate VH and VL domains can be joined with a peptide linker of appropriate composition and length (usually consisting of more than 12 amino acid residues) to form a single-chain Fv (scFv) with binding activity. Methods of manufacturing scFv-based agents of multivalency and multispecificity by varying the linker length were disclosed in U.S. Pat. No. 5,844,094, U.S. Pat. No. 5,837,242 and WO 98/44001. Common problems that have been frequently associated with generating scFv-based agents of multivalency and multispecificity are low expression levels, heterogeneous products, instability in solution leading to aggregates, instability in serum, and impaired affinity.
Several bispecific antibodies targeting CD3 and CD19 are in clinical development. An scFv-based bispecific antibody construct, known as BITE® (Bispecific T-cell Engager), employs a single polypeptide containing 2 antigen-binding specificities, each contributed by a cognate VH and VL, linked in tandem via a flexible linker (see, e.g., Nagorsen et al., 2009, Leukemia & Lymphoma 50:886-91; Amann et al., 2009, J Immunother 32:453-64; Baeuerle and Reinhardt, 2009, Cancer Res 69:4941-44). Another bispecific antibody called DART® (Dual-Affinity Re-Targeting) utilizes a disulfide-stabilized diabody design (see, e.g., Moore et al., 2011, Blood 117:4542-51; Veri et al., 2010, Arthritis Rheum 62:1933-43). Both BITE® and DART® exhibit fast blood clearance due to their small size (˜55 kDa), which requires frequent administration to maintain therapeutic levels of the bispecific antibodies.
Interferons are critical role players in the antitumor and antimicrobial host defense, and have been extensively explored as therapeutic agents for cancer and infectious disease (Billiau et al., 2006, Cytokine Growth Factor Rev 17:381-409; Pestka et al., 2004, Immunol Rev 202:8-32). Despite considerable efforts with type I and II interferons (IFN-α/β and γ), their use in clinic settings have been limited because of the short circulation half-life, systemic toxicity, and suboptimal responses in patients (Pestka et al., 2004, Immunol Rev 202:8-32; Miller et al., 2009, Ann N Y Acad Sci 1182:69-79). The discovery of the IFN-λ family in early 2003 brought an exciting new opportunity to develop alternative IFN agents for these unmet clinical indications (Kotenko et al., 2003, Nat Immunol 4:69-77; Sheppard et al., 2003, Nat Immunol 4:63-8).
The therapeutic effectiveness of IFNs has been validated to date by the approval of IFN-α2 for treating hairy cell leukemia, chronic myelogenous leukemia, malignant melanoma, follicular lymphoma, condylomata acuminata, AIDs-related Kaposi sarcoma, and chronic hepatitis B and C; IFN-β for treating multiple sclerosis; and IFN-γ for treating chronic granulomatous disease and malignant osteopetrosis. Despite a vast literature on this group of autocrine and paracrine cytokines, their functions in health and disease are still being elucidated, including more effective and novel forms being introduced clinically (Pestka, 2007, J. Biol. Chem 282:20047-51; Vilcek, 2006, Immunity 25:343-48). The effects of combination of various interferons with antibody-based therapies also remain under investigation.
Antibody-drug conjugates (ADCs) are a potent class of therapeutic constructs that allow targeted delivery of cytotoxic agents to target cells, such as cancer cells. Because of the targeting function, these compounds show a much higher therapeutic index compared to the same systemically delivered agents. ADCs have been developed as intact antibodies or antibody fragments, such as scFvs. The antibody or fragment is linked to one or more copies of drug via a linker that is stable under physiological conditions, but that may be cleaved once inside the target cell. ADCs approved for therapeutic use include gemtuzumab ozogamicin for AML (subsequently withdrawn from the market), brentuximab vedotin for ALCL and Hodgkin lymphoma, and trastuzumab emtansine for HER2-positive metastatic breast cancer (Verma et al., 2012, N Engl J Med 367:1783-91; Bross et al., 2001, Clin Cancer Res 7:1490-96; Francisco et al., 2003, Blood 102:1458-65). Numerous other candidate ADCs are currently in clinical testing, such as inotuzumab ozogamicin (Pfizer), glembatumomab vedotin (Celldex Therapeutics), SAR3419 (Sanofi-Aventis), SAR56658 (Sanofi-Aventis), AMG-172 (Amgen), AMG-595 (Amgen), BAY-94-9343 (Bayer), BIIB015 (Biogen Idec), BT062 (Biotest), SGN-75 (Seattle Genetics), SGN-CD19A (Seattle Genetics), vorsetuzumab mafodotin (Seattle Genetics), ABT-414 (AbbVie), ASG-5ME (Agensys), ASG-22ME (Agensys), ASG-16M8F (Agensys), IMGN-529 (ImmunoGen), IMGN-853 (ImmunoGen), MDX-1203 (Medarex), MLN-0264 (Millenium), RG-7450 (Roche/Genentech), RG-7458 (Roche/Genentech), RG-7593 (Roche/Genentech), RG-7596 (Roche/Genentech), RG-7598 (Roche/Genentech), RG-7599 (Roche/Genentech), RG-7600 (Roche/Genentech), RG-7636 (Roche/Genentech), anti-PSMA ADC (Progenics), lorvotuzumab mertansine (ImmunoGen), milatuzumab-doxorubicin (Immunomedics), IMMU-130 (Immunomedics), IMMU-132 (Immunomedics) and antibody conjugates of pro-2-pyrrolinodoxorubicin. (See, e.g., Li et al., 2013, Drug Disc Ther 7:178-84; Firer & Gellerman, J Hematol Oncol 5:70; Beck et al., 2010, Discov Med 10:329-39; Mullard, 2013, Nature Rev Drug Discovery 12:329, Provisional U.S. Patent Application 61/761,845.) Because of the potential of ADCs to act as potent anti-cancer agents with reduced systemic toxicity, they may be used either alone or as an adjunct therapy to reduce tumor burden.
Another promising approach to immunotherapy concerns use of antagonistic antibodies against immune checkpoint proteins (e.g., Pardoll, 2012, Nature Reviews Cancer 12:252-64). Immune checkpoints function as endogenous inhibitory pathways for immune system function that act to maintain self-tolerance and to modulate the duration and extent of immune response to antigenic stimulation (Pardoll, 2012). However, it appears that tumor tissues and possibly certain pathogens may co-opt the checkpoint system to reduce the effectiveness of host immune response, resulting in tumor growth and/or chronic infection (see, e.g., Pardoll, 2012, Nature Reviews Cancer 12:252-64; Nirschl & Drake, 2013, Clin Cancer Res 19:4917-24). Checkpoint molecules include CTLA4 (cytotoxic T lymphocyte antigen-4), PD1 (programmed cell death protein 1), PD-L1 (programmed cell death ligand 1), LAG-3 (lymphocyte activation gene-3), TIM-3 (T cell immunoglobulin and mucin protein-3) and several others (Pardoll, 2012, Nature Reviews Cancer 12:252-64; Nirschl & Drake, 2013, Clin Cancer Res 19:4917-24). Antibodies against several of the checkpoint proteins (CTLA4, PD1, PD-L1) are in clinical trials and has shown unexpected efficacy against tumors that were resistant to standard treatments.
A need exists for methods and compositions to generate improved bispecific antibody complexes with longer T1/2, better pharmacokinetic properties, increased in vivo stability and/or improved in vivo efficacy. A further need exists for combination therapies to improve efficacy of treatments directed to inducing immune response against various diseases, such as Trop-2+ cancer.